The vastly prolific McCutchan--author of the Simon Shard series (12 books), the Halfhyde series (16), the Donald Cameron (13), the Commander Shaw (20) and 22 other books--here tells a sixth tale featuring Commodore John Mason Kemp. Once the skipper of a passenger liner, Kemp is now in charge of a convoy heading home from the Indian Ocean in WW II. Along with vital supplies, the convoy picks up colonial troops, civilians and German POWs in East Africa, encounters U-boat danger all along the way, and is unsettled by tensions among the crew, passengers and POWs. The ``Upstairs, Downstairs''-like shipboard mix (including a mostly bonkers Brigadier, a girl no better than she should be and a sad old colonial military couple facing a penurious future) is handled smoothly, as is news from the home front (the chief steward hears that his young wife has been unfaithful to him and Kemp learns that one of his sons is missing in action). The climactic battle with a Nazi surface raider in the South Atlantic is terrific, and ends the novel with a satisfying, surprising bang. (Sept.)